Battery module of improved safety and middle or large-sized battery pack containing the same

ABSTRACT

Disclosed herein is a high-power, large-capacity battery module including a plurality of battery cells or unit modules connected in series to each other such that the battery cells or the unit modules are stacked while being in tight contact with each other or being adjacent to each other, wherein the battery module is fixed such that the stacked state of the battery cells or the unit modules is maintained even when the volume of the battery cells or the unit modules changes at the time of charging and discharging the battery cells or the unit modules, and a portion of an electrode terminal connection region between the battery cells or between the unit modules is weak with respect to the volume expansion of the battery cells or the unit modules such that an expansion stress caused by the swelling of the battery cells is concentrated on the electrode terminal connection region, whereby the electrode terminal connection region is broken, and therefore, an electrical cut-off occurs at the electrode terminal connection region, when the swelling exceeds a predetermined value.

This application is a Continuation of copending application Ser. No.12/673,018 filed on Aug. 11, 2010, which is the U.S. National Phase ofPCT/KR2008/006390, filed Oct. 30, 2008, and which claims priority toApplication No. 10-2007-0119071 filed in Korea, on Nov. 21, 2007. Theentire contents of all of the above applications is hereby incorporatedby reference.

FIELD OF THE INVENTION

The present invention relates to a battery module of improved safety,and, more particularly, to a high-power, large-capacity battery moduleincluding a plurality of battery cells or unit modules connected inseries to each other such that the battery cells or the unit modules arestacked while being in tight contact with each other or being adjacentto each other, wherein the battery module is fixed such that the stackedstate of the battery cells or the unit modules is maintained even whenthe volume of the battery cells or the unit modules changes at the timeof charging and discharging the battery cells or the unit modules, and aportion of an electrode terminal connection region between the batterycells or between the unit modules is weak with respect to the volumeexpansion of the battery cells or the unit modules such that anexpansion stress caused by the swelling of the battery cells isconcentrated on the electrode terminal connection region, whereby theelectrode terminal connection region is broken, and therefore, anelectrical cut-off occurs at the electrode terminal connection region,when the swelling exceeds a predetermined value.

BACKGROUND OF THE INVENTION

As mobile devices have been increasingly developed, and the demand ofsuch mobile devices has increased, the demand of secondary batteries hasalso sharply increased as an energy source for the mobile devices. Amongthem is a lithium secondary battery having high energy density and highdischarge voltage, on which much research has been carried out and whichis now commercially and widely used.

A secondary battery has attracted considerable attention as an energysource for power-driven devices, such as electric bicycles (E-bikes),electric vehicles (EVs), or hybrid electric vehicles (HEVs), as well asan energy source for mobile wireless electronic devices, such as mobilephones, digital cameras, personal digital assistants (PDAs), and laptopcomputers.

A small-sized battery pack having a battery cell packed therein is usedfor small-sized devices, such as mobile phones and digital cameras. Onthe other hand, a middle- or large-sized battery pack having a batterypack, which includes two or more battery cells (hereinafter,occasionally referred to as a “multi-cell”) connected in parallel and/orin series to each other, packed therein is used for middle- orlarge-sized devices, such as laptop computers and electric vehicles.

As previously described, a lithium secondary battery exhibits excellentelectrical properties; however, the lithium secondary battery has lowsafety. For example, when abnormal operations, such as overcharge,overdischarge, exposure to high temperature, and electrical shortcircuits, of the lithium secondary battery occur, decomposition ofactive materials and an electrolyte, which are components of thebattery, is caused, with the result that heat and gas are generated, andthe high-temperature and high-pressure condition caused by thegeneration of the heat and the gas accelerates the above-mentioneddecomposition. Eventually, a fire or explosion may occur.

For this reason, the lithium secondary battery is provided with a safetysystem, such as a protection circuit for interrupting electric currentduring overcharge, overdischarge, or overcurrent of the battery, apositive temperature coefficient (PTC) element whose resistance greatlyincreases so as to interrupt electric current when the temperature ofthe battery increases, and a safety vent for interrupting electriccurrent or discharging gas when pressure increases due to the generationof the gas. In the case of a small-sized cylindrical secondary battery,for example, the PTC element and the safety vent are usually disposed atthe top of an electrode assembly (a generating element) having acathode/separator/anode structure, which is mounted in a cylindricalcase. In the case of a prismatic or pouch-shaped small-sized secondarybattery, on the other hand, the protection circuit module and the PTCelement are usually mounted at the upper end of a prismatic case or apouch-shaped case, in which the generating element is mounted in asealed state.

The safety-related problem of the lithium secondary battery is even moreserious for a middle- or large-sized battery pack having a multi-cellstructure. Since a plurality of battery cells are used in the multi-cellstructure battery pack, the abnormal operation of some of the batterycells may cause the abnormal operation of the other battery cells, withthe result that a fire or explosion may occur, which may lead to alarge-scale accident. For this reason, the middle- or large-sizedbattery pack is provided with a safety system, such as a fuse, abimetal, and a battery management system (BMS), for protecting thebattery cells from the overcharge, the overdischarge, and theovercurrent.

However, as the lithium secondary battery is continuously used, i.e., asthe lithium secondary battery is continuously charged and discharged,the generating element and the electrically connecting members aregradually degraded. For example, the degradation of the generatingelement leads to the decomposition of the electrode material and theelectrolyte, by which gas is generated. As a result, the battery cell(the cylindrical, prismatic, or pouch-shaped case) gradually swells. Inthe normal state of the lithium secondary battery, the safety system,i.e., the BMS detects the overdischarge, the overcharge, and theovercurrent, and controls/protects the battery pack. In the abnormalstate of the lithium secondary battery, however, when the BMS does notoperate, a possibility of danger increases, and it is difficult tocontrol the battery pack for securing the safety of the battery pack.The middle- or large-sized battery pack is generally constructed in astructure in which a plurality of battery cells is fixedly mounted in apredetermined case. As a result, the respective swelling battery cellsare further pressurized in the restrictive case, and therefore, apossibility of a fire or explosion greatly increases under the abnormaloperation condition of the battery pack.

In connection with this case, FIG. 1 is a circuit diagram typicallyillustrating a conventional middle- or large-sized battery pack.Referring to FIG. 1, the conventional middle- or large-sized batterypack 900 includes a battery module assembly 500 constituted by aplurality of battery cells, a BMS 600 for detecting and controlling theoperation of the battery module assembly 500, and a power switch unit(relay) 700 for connecting the battery module assembly 500 and anexternal input and output circuit (inverter) 800 to each other ordisconnecting the battery module assembly 500 and the external input andoutput circuit 800 from each other according to an operation commandfrom the BMS 600.

The BMS 600 maintains the power switch unit 700 to be on in a normaloperation condition of the battery module assembly 500. When theabnormality of the battery module assembly 500 is detected, the BMS 600switches the power switch unit 700 to become off such that the chargingand discharging operation of the battery module assembly 500 isinterrupted. On the other hand, when the BMS abnormally operates or doesnot operate, no control is carried out by the BMS 600, and therefore,the power switch unit 700 is maintained on. As a result, the chargingand discharging operation of the battery module assembly 500 iscontinuously carried out even in a normal operation condition of thebattery module assembly 500.

Therefore, there is a high necessity for a technology that is capable offundamentally securing the safety of the middle- or large-sized batterypack while solving the above problems.

SUMMARY OF THE INVENTION

Therefore, the present invention has been made to solve the aboveproblems, and other technical problems that have yet to be resolved.

As a result of a variety of extensive and intensive studies andexperiments to solve the problems as described above, the inventors ofthe present invention have found that, in case of a battery module beingconstructed in a structure in which a portion of an electrode terminalconnection region between battery cells is weak with respect to thevolume expansion of the battery cells due to the swelling of the batterycells, an expansion stress caused by the swelling of the battery cellsis concentrated on the weak region, when the battery cells swell due toan abnormal operation, such as overcharge, overdischarge, orovercurrent, of the battery module or due to the deterioration of thebattery cells caused by the charge and discharge of the battery cellsfor a long time, with the result that the electrode terminal connectionregion is broken, and therefore, an electrical cut-off occurs at theelectrode terminal connection region, thereby securing the safety of thebattery module to a desired level.

Therefore, it is an object of the present invention to provide a batterymodule of a specific structure to improve safety and a middle- orlarge-sized battery pack including the same.

In accordance with one aspect of the present invention, the above andother objects can be accomplished by the provision of a high-power,large-capacity battery module including a plurality of battery cells orunit modules connected in series to each other such that the batterycells or the unit modules are stacked while being in tight contact witheach other or being adjacent to each other, wherein the battery moduleis fixed such that the stacked state of the battery cells or the unitmodules is maintained even when the volume of the battery cells or theunit modules changes at the time of charging and discharging the batterycells or the unit modules, and a portion of an electrode terminalconnection region between the battery cells or between the unit modulesis weak with respect to the volume expansion of the battery cells or theunit modules such that an expansion stress caused by the swelling of thebattery cells is concentrated on the electrode terminal connectionregion, whereby the electrode terminal connection region is broken, andtherefore, an electrical cut-off occurs at the electrode terminalconnection region, when the swelling exceeds a predetermined value.

In the battery module, constructed in a structure in which the batterycells or the unit modules are stacked, the battery cells are expanded bythe swelling of the battery cells due to an abnormal operation, such asovercharge, overdischarge, or overcurrent, of the battery module or dueto the deterioration of the battery cells caused by the charge anddischarge of the battery cells for a long time, as previously described,and the expansion of the battery cells causes the combustion andexplosion of the battery module.

For this reason, the battery module according to the present inventionis constructed in a structure in which the electrode terminal connectionregion between the battery cells or between the unit modules is weakwith respect to the volume expansion of the battery cells when thebattery cells swell. Consequently, when the swelling exceeds thepredetermined value, e.g., a limit value, the expansion stress isconcentrated on the electrode terminal connection region, whereby theelectrode terminal connection region is physically deformed, e.g.,broken. By the breakage of the electrode terminal connection region, theelectrical connection in the battery module is interrupted, andtherefore, the charging and discharging operation is stopped, with theresult that further swelling of the battery cells or the unit modules isrestrained. Consequently, the combustion or explosion of the batterymodule is prevented, whereby the safety of the battery module is greatlyimproved.

In an exemplary embodiment, the battery cells or the unit modules,constituting the battery module according to the present invention, arecovered by a case, and a partial opening or a notch is formed at apredetermined region of the case corresponding to the electrode terminalconnection region, which is broken when the swelling of the batterycells is excessive. That is, a portion of the case corresponding to theelectrode terminal connection region is formed in the shape of anopening or a notch which is weak with respect to the expansion stresssuch that the excessive expansion stress of the battery cells caused bythe swelling of the battery cells is concentrated on the opening regionor the notch region corresponding to the electrode terminal connectionregion.

The case may be a high-strength case or a sealing member. As an exampleof the latter, a plurality of battery cells or unit modules are mountedin a predetermined frame member, and a sealing member is mounted to theoutside of the frame member. When the sealing member is made of a heatinsulating material, it is possible to restrain the occurrence of thetemperature difference between the battery cells or the unit modules dueto the exposure of some of the battery cells or the unit modules to theoutside.

It is sufficient for the electrode terminal connection region exposedthrough the cutout part or the electrode terminal connection regionlocated at a position corresponding to the notch part to have a size tocause an intended electrical cut-off when the battery cells or thebattery modules swell. Consequently, the electrode terminal connectionregion may be wholly exposed. Alternatively, only a portion of theelectrode terminal connection region may be exposed.

In this specification, the structure of the notch is not particularlyrestricted so long as the notch is easily broken when the battery cellsor the battery modules swell. For example, the notch may be configuredin a structure formed by partially cutting a portion of the region ofthe case or the sealing member corresponding to the electrode terminalconnection region in the shape of a slit or in a thin and long groovestructure having a relatively small thickness.

As a concrete example of the structure, each of the unit modulesincludes battery cells, having electrode terminals connected in seriesto each other, constructed in a stacked structure in which a connectionpart between the electrode terminals is bent, and a pair ofhigh-strength cell covers coupled to each other for covering the outersurfaces of the battery cells except the electrode terminals, and acutout part or a notch part configured in a shape to induce localdeformation of the battery cells, when the battery cells swell, isformed at a predetermined region of at least one of the cell coversadjacent to the electrode terminal connection region.

For example, battery cells may be covered by high-strength cell covers,made of synthetic resin or metal, to constitute a unit module. Thehigh-strength cell covers serve to protect the battery cells, whichexhibit low strength and, at the same time, to restrain the change inrepetitive expansion and contraction of the battery cells during thecharge and discharge of the battery cells, thereby preventing thebreakage of sealing regions of the respective battery cells. Adesired-shaped cutout part or a notch part is formed at a portion of atleast one of the cell covers adjacent to the electrode terminalconnection region such that an expansion stress caused by the swellingof the battery cells is concentrated on the electrode terminalconnection region corresponding to the cutout part or the notch part ofthe cell cover.

For example, the battery module may include a plurality of unit modulesof which each includes plate-shaped battery cells each having electrodeterminals formed at the front and rear sides of a battery case. In thisstructure, the unit modules may be mounted in the case in a structure inwhich the unit modules are erected in the lateral direction while beingspaced a predetermined distance from each other such that a coolant canflow through the space to cool the unit modules. In this structure, thecutout part or the notch part may be formed at a cell cover of theoutermost unit module. Consequently, the expansion stress of the batterycells due to the abnormal operation of the battery cells is concentratedon the cutout part or the notch part formed at the cell cover of theoutermost unit module, with the result that the electrode terminalconnection region between the battery cells of the outermost unit moduleis broken, whereby the electrical connection for charging anddischarging is interrupted.

The size of the cutout part or the notch part may be changed dependingupon the breakage setting conditions of the electrode terminalconnection region. Preferably, the size of the cutout part or the notchpart is set such that the electrode terminal connection region is brokenwhen the swelling of the battery cells brings about the increases involume of the battery cells equivalent to 1.5 to 5 times the thicknessof each battery cell. The setting range may be changed based on thesafety test standard of a desired battery module. However, when the sizeof the of the cutout part or the notch part is too large, the mechanicalstrength of the battery cells achieved by the cell covers may decrease,and the expansion of the battery cells may not be properly restrained ina normal operation condition. Therefore, it is necessary to set the sizeof the cutout part or the notch part within an appropriate range inconsideration of the above-mentioned respects.

In accordance with another aspect of the present invention, there isprovided a middle- or large-sized battery pack including the batterymodule as described above.

Specifically, the middle- or large-sized battery pack according to thepresent invention includes a battery module, a battery management system(BMS) for detecting and controlling the operation of the battery module,and a power switch unit located between the battery module and anexternal input and output circuit for connecting the battery module andthe external input and output circuit to each other or disconnecting thebattery module and the external input and output circuit from each otheraccording to an operation command from the BMS. The connection betweenthe battery module and the power switch unit is interruptedindependently from the BMS in an abnormal operation condition.

In the conventional middle- or large-sized battery pack, as previouslydescribed with reference to FIG. 1, the connection between the batterymodule and the external input and output circuit is interrupted by thepower switch unit under the control of the BMS, when overcurrent orovervoltage occurs in the battery module, and therefore, the occurrenceof the safety-related problems due to the overcurrent or the overvoltageis prevented.

However, when the BMS abnormally operates or does not operate, it is notpossible for the BMS to control the power switch unit, with the resultthat the battery module under the abnormal condition is connected to theexternal input and output circuit, which leads to a serious situation.

On the other hand, the middle- or large-sized battery pack according tothe present invention is constructed in a structure in which theconnection between the battery module and the power switch unit isinterrupted independently from the BMS in an abnormal operationcondition. Consequently, when an abnormal operation, such as overcharge,overdischarge, or overcurrent, of the battery module occurs, theelectrode terminal connection region is broken and short-circuited dueto the expansion stress of the battery cells due to the swelling of thebattery cells, as previously described, and therefore, the supply ofpower to the battery module is interrupted. As a result, the electricalconduction between the battery module and the external input and outputcircuit is prevented even when the BMS abnormally operates or does notoperate.

For reference, the external input and output circuit may be connected toan external device, such as a motor or an electronic device of avehicle. For example, the external input and output circuit may be aninverter that converts direct current electricity into alternatingcurrent electricity. Also, the power switch unit may be a relay.

In an exemplary embodiment, the middle- or large-sized battery pack isconstructed in a structure in which a plurality of battery modules arefixed by a frame member, outermost battery modules are covered bysealing members fixed to the frame member, and cutout parts or notchparts configured in a shape to induce local deformation of the batterymodules when the battery modules swell are formed at predeterminedregions of the sealing members adjacent to an electrode terminalconnection region.

That is, the predetermined-shaped cutout parts or thepredetermined-shaped notch parts are formed at predetermined regions ofthe sealing members adjacent to an electrode terminal connection regionsuch that an expansion stress caused by the swelling of the batterymodules is concentrated on the cutout parts or the notch parts of thesealing members.

Consequently, the electrode terminal connection region between thebattery cells or the unit modules of each outermost battery moduleextrudes outside through the corresponding cutout part or through thebroken notch part. The swelling volume of the protruding electrodeterminal connection region continuously increases, and, when theswelling volume reaches a predetermined critical breakage value, theelectrode terminal connection region is broken, with the result that theconnection between the electrode terminals is interrupted, therebysecuring the safety of the battery pack.

In the above-described structure, the sealing members may be made of aheat insulating material to further increase the uniformity between thebattery modules. In particular, the sealing members may be made of foamresin to minimize the total weight of the battery pack and, at the sametime, to improve heat insulation.

As a concrete example of such a structure, the battery pack includes abattery module assembly including a plurality of rectangular batterymodules, each of which includes a plurality of battery cells or unitmodules connected in series to each other, stacked by twos or more inthe lateral direction (the vertical direction) and the height direction(the horizontal direction) such that the battery cells or the unitmodules are generally configured in a hexahedral structure (a hexahedralstack), outer edges of the hexahedral stack being fixed by the framemember, and a BMS mounted at an orientation surface of input and outputterminals, a surface opposite to the orientation surface, or a surfaceat a side of the orientation surface, for controlling the operation ofthe battery modules. The battery cells of the unit modules in each ofthe rectangular battery modules are arranged in parallel to a pair ofopposite surfaces (a, d) of the hexahedral stack, and a sealing memberhaving the cutout part or the notch part is mounted at least one of theopposite surfaces (a, d) of the hexahedral stack.

In the middle- or large-sized battery pack, the plurality of rectangularbattery modules are stacked in the vertical direction and in thehorizontal direction to constitute the hexahedral stack, and thehexahedral stack is fixed by the frame member. Consequently, the middle-or large-sized battery pack is generally constructed in a compact andstable structure. Also, the mechanical coupling and the electricalconnection of the middle- or large-sized battery pack are achievedwithout using a large number of members.

Each of the rectangular battery modules, constituting the hexahedralstack, is constructed in a structure in which the plurality of batterycells or unit modules are connected in series to each other, aspreviously described. For example, two or more plate-shaped batterycells are stacked to constitute each rectangular battery module.Preferably, two or more unit modules are stacked to constitute eachrectangular battery module.

Also, the BMS, which is a system for controlling the operation of thebattery modules, is mounted at a surface where the input and outputterminals are located (a terminal orientation surface), a surfaceopposite to the orientation surface, or a surface at a side of theorientation surface. Consequently, the connection between the BMS andthe input and output terminals is easily achieved, the electricalconnection structure and thus the assembling process thereof are furthersimplified, the increase of internal resistance is prevented through thereduction in length of an electrical connection member, and apossibility of the connection member short circuiting due to externalimpact decreases.

Since the battery cells of the unit modules in each of the rectangularbattery modules are arranged in parallel to the pair of oppositesurfaces (a, d) of the hexahedral stack to achieve high spatialutilization, the rectangular battery modules are also arranged inparallel to the pair of opposite surfaces (a, d) of the hexahedralstack, and the cutout parts or the notch parts are formed at the sealingmembers mounted at the opposite surfaces (a, d), whereby localdeformation of the swelling battery modules is easily induced at theelectrode terminal connection region.

In the above-described structure, the frame member for fixing the outeredges of the hexahedral stack, constituted by the rectangular batterymodules, may be configured in various structures. For example, the framemember may be configured in a structure in which a plurality of framepieces integrally coupled to each other such that each frame piece fixescorresponding one of 12 edges of the hexahedral stack or in a structurein which a plurality of frames integrally coupled to each other suchthat each frame fixes at least four edges of the hexahedral stack on thesame plane.

Specifically, the frames fixing the four edges located at opposite sidesof the hexahedral stack in the lateral direction are constructed in anintegrated structure, and the remaining individual frame pieces arecoupled to the integrated frames. In this coupling structure, forexample, the upper-row rectangular battery modules are fixed by twoindividual frame pieces, the lower-row rectangular battery modules arefixed by the remaining two individual frame pieces, and the twointegrated frames are coupled to the four individual frame pieces. Inthis way, the fabrication of the battery module assembly is easilyachieved, thereby improving the fabrication efficiency.

The middle- or large-sized battery pack according to the presentinvention may be used as a power source for electric vehicles, hybridelectric vehicles, etc., which have a limited installation space and areexposed to frequent vibration and strong impact, in consideration of theinstallation efficiency and structural stability of the battery pack.

In accordance with another aspect of the present invention, there isprovided a method of securing the safety of a high-power, large-capacitybattery module or a battery pack, the battery module including aplurality of battery cells or unit modules connected in series to eachother such that the battery cells or the unit modules are stacked whilebeing in tight contact with each other or being adjacent to each other,the battery pack including a plurality of the battery modules connectedin series or in parallel to each other, the method includingconcentrating an expansion stress on an electrode terminal connectionregion between the battery cells or the unit modules, when the batterycells excessively swell, whereby the electrode terminal connectionregion is broken, and therefore, an electrical cut-off occurs at theelectrode terminal connection region.

By using this method, it is possible to break the electrical connectionstructure in the battery module and thus prevent the combustion orexplosion of the battery pack when the battery module abnormallyoperates or the battery module is deviated from its appropriateoperation state as a result of excessive use of the battery module, aspreviously described, although the BMS, which is the charging anddischarging control system, does not operate or abnormally operates.

In accordance with a further aspect of the present invention, there isprovided a battery pack including high-power, large-capacity batterymodules connected in series or in parallel to each other, each of thebattery modules including a plurality of battery cells or unit modulesconnected in series to each other such that the battery cells or theunit modules are stacked while being in tight contact with each other orbeing adjacent to each other, wherein the battery pack is constructed ina structure in which pressure, generated in the battery cells when thebattery cells are overcharged, is concentrated on weak parts of thebattery cells or the unit modules, such that the weak parts are broken,and therefore, an electrical cut-off occurs at the weak parts, wherebythe safety of the battery pack is secured.

Since the battery pack includes the weak parts configured in a specificstructure, the internal pressure of the battery cells is induced at theweak parts, when the battery cells are overcharged, with the result thatan electrical cut-off occurs at the weak parts, whereby the safety ofthe battery pack is greatly improved.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a circuit diagram typically illustrating a conventionalmiddle- or large-sized battery pack;

FIG. 2 is a perspective view illustrating a battery module according toan exemplary embodiment of the present invention;

FIGS. 3 and 4 are perspective views illustrating a pair of battery cellsand cell covers constituting a unit module;

FIG. 5 is a perspective view illustrating a unit module stack;

FIG. 6 is a perspective view illustrating a battery module assemblyaccording to another exemplary embodiment of the present invention;

FIG. 7 is a perspective view illustrating the middle- or large-sizedbattery pack from which a battery module assembly is removed;

FIG. 8 is a circuit diagram typically illustrating a middle- orlarge-sized battery pack according to another exemplary embodiment ofthe present invention;

FIG. 9 is an experimental picture of a middle- or large-sized batterypack illustrating that an electrode terminal is broken by swelling;

FIG. 10 is a perspective view illustrating a middle- or large-sizedbattery pack according to a further exemplary embodiment of the presentinvention;

FIG. 11 is a perspective view illustrating a sealing member of FIG. 10;and

FIG. 12 is a vertical sectional view illustrating region A of FIG. 11.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Now, exemplary embodiments of the present invention will be described indetail with reference to the accompanying drawings. It should be noted,however, that the scope of the present invention is not limited by theillustrated embodiments.

FIG. 2 is a perspective view typically illustrating a battery moduleaccording to an exemplary embodiment of the present invention.

Referring to FIG. 2, the battery module 100′ is constructed in astructure in which a unit module stack 200 is mounted between an uppercase 120 and a lower case 130, which are assembled to each othervertically, while the unit module stack 200 is erected on the sidethereof. At the front of the upper case 120 is formed an input andoutput terminal 140. At the front of the lower case 130 is formed a busbar 150 electrically connected to the input and output terminal 140. Atthe rear of the lower case 130 is mounted a connector 160 to which avoltage and temperature sensor is connected.

In the unit module stack 200, a cutout part 212 is formed in a cellcover of the outermost unit module 210. Consequently, when a batterycell is swelled by gas generated in the battery cell due to a shortcircuit or overcharge of the battery cell, the local deformation of abattery cell is induced at the cutout part 212.

FIGS. 3 and 4 are perspective views typically illustrating a pair ofbattery cells and cell covers constituting a unit module.

The unit module (not shown) is constructed in a structure in which twobattery cells 302 and 304 are connected in series to each other, and thebattery cells 302 and 304 are covered by high-strength cell covers 310while electrode terminals 305 and 306 are bent. The cell covers 310 arecoupled to each other to cover the outer surfaces of the battery cells302 and 304 excluding the electrode terminals 305 and 306. In a regionof one of the cell covers 310 adjacent to electrode terminal connectionregion 314 of the battery cells 302 and 304 is formed a cutout part 312,which is obtained by cutting out a portion of the corresponding cellcover 310. Consequently, when the battery cells 302 and 304 swell, theelectrode terminal connection region 314 protrudes out of the cutoutpart 312 and is deformed.

FIG. 5 is a perspective view typically illustrating a unit module stack.

Referring to FIG. 5, the unit module stack 200 is constructed in astructure in which four unit modules 202, 203, 204, and 205, each ofwhich is manufactured in a structure in which battery cells are coveredby corresponding cell covers, are stacked in a zigzag fashion while theunit modules 202, 203, 204, and 205 are connected in series to eachother. In one of the cell covers covering the outermost unit module 202,among the unit modules 202, 203, 204, and 205, is formed a predeterminedshaped cutout part 316, which is located at a region 318 adjacent to anelectrode terminal connection region.

FIG. 6 is a perspective view typically illustrating a battery moduleassembly according to another exemplary embodiment of the presentinvention, and FIG. 7 is a perspective view typically illustrating themiddle- or large-sized battery pack from which a battery module assemblyis removed.

Referring to these drawings, the middle- or large-sized battery pack isconstructed in a structure in which a power switch unit 600 and abattery management system (BMS) 700 are mounted at one side of a batterymodule assembly 500′ including a hexahedral stack 400 constituted by sixrectangular battery modules 101, 102, 103, 104, 105, and 106 and a framemember 510 for fixing outer edges of the hexahedral stack 400. Themiddle- or large-sized battery pack is generally formed in the shape ofa rectangular parallelepiped.

The six rectangular battery modules 101, 102, 103, 104, 105, and 106 arestacked in a manner in which every two battery modules are stacked inthe horizontal direction and every three battery modules are stacked inthe vertical direction. Also, the rectangular battery modules 101, 102,103, 104, 105, and 106 are stacked in an opposite arrangement structuresuch that input and output terminals 240 formed at one-side surfaces ofthe battery modules are adjacent to each other. That is, the upper-rowbattery modules 101, 102, and 103 are stacked on the correspondinglower-row battery modules 104, 105, and 106 in a state in which theupper-row battery modules 101, 102, and 103 turn upside down such thatthe upper-row battery modules 101, 102, and 103 and the correspondinglower-row battery modules 104, 105, and 106 are symmetrical to eachother along an imaginary center line.

The frame member 510 is constructed in a structure in which a pluralityof frames are coupled to one another to stably fix twelve outer edges ofthe hexahedral stack 400. In a state in which the hexahedral stack 400is mounted in the frame member 510, six surfaces of the hexahedral stack400 are exposed to the outside.

The power switch unit 600 and the BMS 700, which serve to conductelectric current, if necessary, for performing a charging anddischarging operation, serve to appropriately drop voltage at the timeof commencing the operation of the battery system or duringdecomposition of the battery system, serve to electrically interconnectthe rectangular battery modules 101, 102, 103, 104, 105, and 106, andserve to protect a circuit from overcurrent, overvoltage, etc., aremounted at the front of the hexahedral stack 400 where the input andoutput terminals 240 are located. The input and output terminals 240 ofthe rectangular battery modules 101, 102, 103, 104, 105, and 106 areadjacent to one another. Consequently, it is possible to easily achievethe connection between the input and output terminals 240 and the powerswitch unit 600 and to greatly reduce the length of a member forelectrical connection.

A sealing member 520 having a cutout part 522 formed therein is mountedin the opening of the frame at one side of the front of the hexahedralstack 400 where the power switch unit 600 is mounted. Consequently, theswelling of the outermost battery module 101 is induced at the openingof the cutout part 522, and an electrode terminal connection region 524in the outermost battery module 101 adjacent to the cutout part 522 isbroken or short-circuited by the swelling of the outermost batterymodule 101, thereby securing the safety of the middle- or large-sizedbattery pack.

FIG. 8 is a circuit diagram typically illustrating a middle- orlarge-sized battery pack according to another exemplary embodiment ofthe present invention.

Referring to FIG. 8, the middle- or large-sized battery pack 910includes a battery module assembly 500′, a BMS 600 for detecting andcontrolling the operation of the battery module assembly 500′, anexternal input and output circuit 800 connected to an external device,and a power switch unit 700 located between the battery module assembly500′ and the external input and output circuit 800 for connecting thebattery module assembly 500′ and the external input and output circuit800 to each other or disconnecting the battery module assembly 500′ andthe external input and output circuit 800 from each other according tothe operation command from the BMS 600.

The middle- or large-sized battery pack 910 includes an outermost cellcover having the cutout part 212 of FIG. 2 formed therein or a sealingmember 520 having the cutout part 522 of FIG. 6 formed therein.Consequently, when the swelling thickness of the battery cell becomestwice or more the original thickness of the battery cell, the electrodeterminal connection region protrudes into the cutout part 212 or 522,and therefore, the battery cell is short-circuited. As a result, theelectrical connection between the battery module assembly 500′ and thepower switch unit 700 is interrupted, thereby preventing the electricalconduction between the battery module assembly 500′ and the externalinput and output circuit 800.

The inventors of the present invention manufactured a middle- orlarge-sized battery pack based on the structure of FIG. 6, and carriedout overcharge experiments with respect to the manufactured middle- orlarge-sized battery pack to actually confirm the effects acquired byconstructing the middle- or large-sized battery pack according to thepresent invention. The experiment result is shown in FIG. 9.

Referring to FIG. 9, the swelling of the battery cells 302 and 304 wasobserved when the middle- or large-sized battery pack was overcharged.The swelling was concentrated on the cutout part 522 of the sealingmember 520, whereas the swelling was considerably restrained at thesealing member 520 fixed to the frame member 510. As a result, theswelling of the battery cells 302 and 304 at the cutout part 522 reachedapproximately three times the normal thickness of the respective batterycells. By such swelling of the battery cells 302 and 304, the electrodeterminal connection region 318 of the battery cells 302 and 304 wasbroken, with the result that the connection in series between thebattery cells 302 and 304 was interrupted, and therefore, an electricalcut-off occurred. Consequently, the charging operation was no longercarried out.

FIG. 10 is a perspective view typically illustrating a middle- orlarge-sized battery pack according to a further exemplary embodiment ofthe present invention, and FIG. 11 is a perspective view typicallyillustrating a sealing member of FIG. 10.

Referring to these drawings, the middle- or large-sized battery pack 910includes a battery module assembly 502 having six rectangular batterymodules stacked in a two-story structure while being arranged three bythree in the lateral direction (the vertical direction) such that thesix rectangular battery modules are generally configured in a hexahedralstructure (a hexahedral stack), outer edges of the hexahedral stackbeing fixed by a frame member 510′, and a BMS 700′ mounted at one sideof the frame member 510′ corresponding to input and output terminals forcontrolling the operation of the battery modules.

Also, a sealing member 520′ having a notch 522′ formed approximately inthe shape of ‘[’ is mounted at the frame member 510′ where the BMS 700′is located. Consequently, when the battery cells excessively swell, thenotch 522′ of the sealing member 520′ is broken, and therefore, thebattery cells of the outermost battery module protrude outward. As aresult, an electrical cut-off occurs at an electrode terminal connectionregion between the battery cells.

FIG. 12 is a vertical sectional view typically illustrating region A ofFIG. 11.

Referring to FIG. 12, the notch may be configured in a structure 522′formed by partially cutting a portion of the sealing member 520′ in theshape of a slit or in a thin and long groove structure 524′ having arelatively small thickness.

INDUSTRIAL APPLICABILITY

As apparent from the above description, the battery module according tothe present invention is constructed in a structure in which a portionof the electrode terminal connection region between the battery cells isweak with respect to the volume expansion of the battery cells due tothe swelling of the battery cells. As a result, when the battery cellsswell due to an abnormal operation, such as overcharge, overdischarge,or overcurrent, of the battery module or due to the deterioration of thebattery cells caused by the charge and discharge of the battery cellsfor a long time, the electrode terminal connection region is broken andshort-circuited. Consequently, the present invention has the effect ofgreatly improving the safety of the battery module.

Also, the middle- or large-sized battery pack according to the presentinvention is constructed in a structure in which the electricalconnection between the battery module and the power switch unit isinterrupted independently from the BMS. Consequently, the presentinvention has the effect of securing the safety of the battery pack,even when the BMS abnormally operates or does not operate, and, inaddition, greatly improving the reliability of the battery pack.

Although the exemplary embodiments of the present invention have beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

1. A high-power, large-capacity battery module comprising a plurality ofbattery cells or unit modules connected in series to each other suchthat the battery cells or the unit modules are stacked while being intight contact with each other or being adjacent to each other, whereinthe battery module is fixed such that the stacked state of the batterycells or the unit modules is maintained even when the volume of thebattery cells or the unit modules changes at the time of charging anddischarging the battery cells or the unit modules, and a portion of anelectrode terminal connection region between the battery cells orbetween the unit modules is weak with respect to the volume expansion ofthe battery cells or the unit modules such that an expansion stresscaused by the swelling of the battery cells is concentrated on theelectrode terminal connection region, whereby the electrode terminalconnection region is broken, and therefore, an electrical cut-off occursat the electrode terminal connection region, when the swelling exceeds apredetermined value, wherein the battery cells or the unit modules arecovered by a case, and a partial opening or a notch is formed at apredetermined region of the case corresponding to the electrode terminalconnection region, which is broken when the swelling of the batterycells is excessive.
 2. The battery module according to claim 1, whereineach of the unit modules includes battery cells, having electrodeterminals connected in series to each other, constructed in a stackedstructure in which a connection part between the electrode terminals isbent, and a pair of high-strength cell covers coupled to each other forcovering the outer surfaces of the battery cells except the electrodeterminals, and a cutout part or a notch part configured in a shape toinduce local deformation of the battery cells when the battery cellsswell is formed at a predetermined region of at least one of the cellcovers adjacent to the electrode terminal connection region.
 3. Thebattery module according to claim 2, wherein the cutout part or thenotch part is formed at a cell cover of the outermost unit module. 4.The battery module according to claim 2, wherein the size of the cutoutpart or the notch part is set such that the electrode terminalconnection region is broken when the swelling of the battery cellsbrings about the increases in volume of the battery cells equivalent to1.5 to 5 times the thickness of each battery cell.
 5. A middle- orlarge-sized battery pack comprising: at least one battery moduleaccording to claim 1; a battery management system (BMS) for detectingand controlling the operation of the at least one battery module; and apower switch unit located between the at least one battery module and anexternal input and output circuit for connecting the at least onebattery module and the external input and output circuit to each otheror disconnecting the at least one battery module and the external inputand output circuit from each other according to an operation commandfrom the BMS, wherein the connection between the at least one batterymodule and the power switch unit is interrupted independently from theBMS in an abnormal operation condition.
 6. The battery pack according toclaim 5, wherein the battery pack is constructed in a structure in whicha plurality of battery modules are fixed by a frame member, outermostbattery modules are covered by sealing members fixed to the framemember, and cutout parts or notch parts configured in a shape to inducelocal deformation of the battery modules when the battery modules swellare formed at predetermined regions of the sealing members adjacent toan electrode terminal connection region.
 7. The battery pack accordingto claim 6, wherein the sealing members are made of a heat insulatingmaterial.
 8. The battery pack according to claim 6, wherein the batterypack comprises: a battery module assembly including a plurality ofrectangular battery modules, each of which includes a plurality ofbattery cells or unit modules connected in series to each other, stackedby twos or more in the lateral direction (the vertical direction) andthe height direction (the horizontal direction) such that the batterycells or the unit modules are generally configured in a hexahedralstructure (a hexahedral stack), outer edges of the hexahedral stackbeing fixed by the frame member; and a BMS mounted at an orientationsurface of input and output terminals, a surface opposite to theorientation surface, or a surface at a side of the orientation surface,for controlling the operation of the battery modules, and wherein thebattery cells of the unit modules in each of the rectangular batterymodules are arranged in parallel to a pair of opposite surfaces of thehexahedral stack, and sealing members having the cutout parts or thenotch parts are mounted at the opposite surfaces of the hexahedralstack.
 9. The battery pack according to claim 8, wherein the framemember includes a plurality of frames integrally coupled to each othersuch that each frame fixes corresponding one of 12 edges of thehexahedral stack or each frame fixes at least four edges of thehexahedral stack on the same plane.
 10. An electric vehicle or a hybridelectric vehicle including the battery pack according to claim 5 as apower source.